The human rights harms of climate change are “already occurring” at +1C (the current level of warming) and are expected to worsen with every incremental increase in temperature. Scientific consensus on climate change informs the assessment of climate action, including what targets and measures are effective or appropriate.

As colleagues and I recently submitted to the Inter-American Court of Human Rights, climate science can not only help inform what targets states or companies should set to meet a Paris Agreement-aligned reduction in emissions – it can also inform judicial scrutiny. Courts should feel empowered to rely on best available science to assess the policies and measures which underpin a climate target to conclude whether these are genuinely capable of helping to achieve that target, or whether they are ineffective or rely too much on unproven technologies, like carbon capture.

April Williamson, Senior Legal Associate at the Climate Litigation Network (a lawyer with a scientific background) highlights “climate science has been critical in litigation cases, to provide courts with an understanding of how greenhouse gas emissions must decline” and to evidence the “current and projected impacts of climate change”. Williamson also explained the “considerable weight” courts have given to the IPCC, which reflects not just the scientific but the political consensus on climate change. Further, “reports by regional and national scientific advisory bodies” have provided more granular insight to “illustrate what can and should be done in terms of emissions reductions” and been “instrumental in providing courts with the evidence required to order governments to take greater action”.

This has been the case in a number of government climate accountability cases, with Pakistani, German, Nepalese, French, Colombian, Belgian, and more apex courts clearly stating when states fell short. It would follow this can be applied to corporate defendants too — the Philippines Human Rights Commission inquiry on the subject concluded so, and a Dutch court recently agreed.

The Hague District Court relied heavily on scientific findings to determine Shell was not, in fact and in law, doing enough to fulfil its obligations around climate. It ordered the company to decrease its emissions by 45% by 2030. “Without strong scientific evidence”, Williamson notes, “it would not have been possible for NGOs, communities and individuals to hold governments and corporations to account in court.”

What about advice to scientists providing evidence in climate cases? Interveners in another recent and successful case (KlimaSeniorinnen v Switzerland) advised their fellow scientists: target evidence specific to the case, use comparators to set climate targets or measures in the wider context, learn from interdisciplinary work and “observe scientific integrity while recognising values”. Meaning, observe scientific integrity while recognising legal principles and existing state duties also inform assessments of, for example, what national “fair shares” should be, and so provide alternative analyses or statements of probabilities. Again, dialogue and collaboration between science and law pave the way.

Looking ahead: building cases and future impacts

The caveat to these wins and positive developments is, of course, that each legal system has its distinctive causes of actions, recognised duties, rules on standing or causation, standards of proof, and legal cultures. However, comparative analysis and insight into past wins and failures can help practitioners understand how corporate climate litigation may successfully be brought in their own jurisdiction.

Climate cases against states have had a “track record of success”: new legislation, investment in renewables, societal discussions, and political parties putting climate action at the centre of policy programmes.

Climate cases against corporates have been shown to impact their share prices. We have also seen an energy company turn around to sue its own former management and insurers after losing a challenge against a proposed coal project investment. Further research has shown climate litigation has resulted in less corporate greenwashing.

As courts continue to assess companies’ climate actions and identify those which fall short, this could have ground-breaking repercussions. Relying on climate science to inform and assess their targets and measures will be key to build a just and effective energy transition without loopholes. One that does not depend on an over-reliance on carbon dioxide removal, but rather is based on emissions reduction and genuine climate action.

For part 1 of the blog on using climate science to establish legal causation, see here.

Lucia Saborio Perez works in human rights and climate litigation, at Leigh Day’s International Department. She recently undertook a clerkship at the European Court of Human Rights and was previously with Greenpeace International’s Legal Unit and the Environmental Defenders Office. She has worked on state and corporate climate accountability cases and advisory proceedings across five continents and at three international courts.